Embodiments of optical sensors have become known in which the distance from an object is determined optically using the time of flight (TOF) method. In this case, an oscillation is modulated onto light emitted from a light source. Moreover, a sensor is provided with which the modulated light be can be detected when it is retro reflected from a corresponding object surface. The distance from the object at which the light has been retro reflected can be determined from the phase difference of the oscillation modulated on between the emitted and the received reflected light. In order to enable an unambiguous evaluation, the wavelength of the oscillation modulated onto the light should be longer than twice the distance from the object at which the light is retro reflected.
Since objects to be detected are regularly poor reflectors, for example, asphalt, marble, human beings, clothing, hand luggage etc., that backscatter only a portion of the light and absorb another portion, only a comparatively small portion of the emitted modulated light returns to the receiver. Light sources of appropriate intensity must be used in order to obtain a light signal that can be evaluated.
Such light sources consist as a rule of LEDs or laser diodes. Since such components are comparatively expensive, it is advantageous to use as few of these components as possible. In order, nonetheless, to ensure a satisfactory light intensity, the components are regularly operated at their physical limits, and this limits the lifetime of the components.
It is known, furthermore, to undertake a distance measurement by evaluating the propagation time of an electromagnetic radiation.